4-Aminodiphenylamine is an important intermediate of antioxidant and stabilizer, and is an important chemical product for rubber industry and polymer industry. Depending on starting materials, current methods for preparing 4-aminodiphenylamine include: (1) aniline method, wherein p-nitro-chlorobenzene and aniline as raw materials react in the presence of a catalyst to produce 4-nitrodiphenylamine, then 4-nitrodiphenylamine is reduced by sodium sulfide to form 4-aminodiphenylamine; (2) formanilide method, wherein formic acid and aniline are used as starting materials to prepare formanilide, which in turn reacts with p-nitro-chlorobenzene in the presence of an acid-binding agent such as potassium carbonate, to produce 4-nitrodiphenylamine, and then 4-nitrodiphenylamine is reduced by sodium sulfide to form 4-aminodiphenylamine; (3) diphenylamine method, wherein diphenylamine as raw material is nitrosated using a nitrite in an organic solvent to produce N-nitrosodiphenyamine, which rearranges to 4-nitrosodiphenyamine hydrochloride under the action of anhydrous hydrogen chloride, then 4-nitrosodiphenyamine hydrochloride is neutralized with a base to give 4-nitrosodiphenyamine, and said 4-nitrosodiphenyamine is finally reduced to 4-aminodiphenylamine by sodium sulfide. Although these methods use different starting materials, traditional sodium sulfide is used as reducing agent to prepare 4-aminodiphenylamine. These reactions suffer from severe reaction conditions, complex operation, higher energy consumption, lower yield, higher cost and environment pollution caused by concomitant waste water, waste gas and waste residue.
Among the preparation methods of 4-aminodiphenylamine, one utilizes nitrobenzene or nitrobenzene and aniline or nitrosobenzene as raw materials to carry out condensation reaction, and then utilizes hydrogen gas to perform hydrogenation to produce 4-aminodiphenylamine. In fact, it was reported in 1901 (Wohl, Chemische Berichte, 34, p. 2442 (1901)) and in 1903 (Wohl, Chemische Berichte, 36, p. 4135 (1903)) that nitrobenzene reacted with aniline under the action of a base to form 4-nitrosodiphenylamine and 4-nitrodiphenylamine. However, said method is neither attached importance to nor developed because of its relatively low yield until 1990s when it is researched and developed again and achieved some progresses (see DE19734055.5, DE19810929.6, and DE19709124.5). The disclosed methods share the following disadvantages: 1) catalysts used are expensive so as to result in excessive high production cost when said catalysts are used in industrial scale production, so that said methods have no advantage in comparison with the current production techniques. For example, tetraalkyl ammonium hydroxide and fluoride used in condensation reaction and noble metal, such as palladium, platinum, rhodium, and the like, used in hydrogenation reaction are expensive. The instability of tetraalkyl ammonium hydroxide imparts some difficulty to recovery and reuse of tetraalkyl ammonium hydroxide. The use of noble metal hydrogenation catalysts applies higher requirements to raw materials and equipments; 2) the yield is relatively low, and only suitable for laboratory research. This is an important reason why said methods are very difficult to be industrialized; 3) operation is complicated, and this isn't in favor of continuous operation and limits the production scale; 4) separation is difficult and purity of product is not high.
U.S. Pat. No. 6,395,933 discloses a process for synthesizing 4-aminodiphenylamine by reacting nitrobenzene and a substituted aniline at a certain temperature in the presence of a strong base and a phase-transfer catalyst. The process is unsatisfactory in yield and there are many side reactions. In the mixture of 4-nitrodiphenylamine and 4-nitrosodiphenylamine produced, the proportion of 4-nitrodiphenylamine is too high so that too much hydrogen is consumed during hydrogenation reaction and the production cost is thereby increased. Furthermore, said process needs an oxidizing agent so that it is not suitable for industrial production.
WO9300324 discloses a process for preparing 4-aminodiphenylamine by reacting nitrobenzene and aniline at a proper temperature in a proper solvent in the presence of a base with the content of proton materials in solution being controlled. Said process requires a solvent and has to control the content of proton materials in solution. The introduction of the solvent results in the increment of energy consumption and separation difficulty. Controlling the content of proton materials gives rise to difficulty of operating and controlling the reaction. In particular, at the later stage of condensation reaction, controlling the content of proton materials in the solution, which mainly means dehydrating to a lower water content, will prolong reaction time and partial aniline will be entrained out. The later stage, the more difficult removing the proton materials. Controlling the proton materials at a certain level is difficult, and goes against industrial production. The expensive tetraalkyl quaternary amine base catalyst will quickly decompose in the course of controlling the content of proton materials to a range of from 0.5 to 4 percent, resulting in the increment of the production cost.